Refrigeration cycle

ABSTRACT

A refrigerating apparatus comprising a refrigeration cycle comprising at least a compressor, a condenser, a dryer, an expansion mechanism and an evaporator, a refrigerant composed mainly of a fluorocarbon type refrigerant containing no chlorine and having a critical temperature of 40° C. or higher, and a refrigerating machine oil comprising as base oil an ester oil of one or more fatty acids which contains at least two ester linkages                    
     in the molecule and has a viscosity at 40° C. of 2 to 70 cSt and a viscosity at 100° C. of 1 to 9 cSt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 09/064,171, filed Apr.22, 1998, now U.S. Pat. No. 6,029,459, which application is a divisionalof Ser. No. 08/610,186, filed Mar. 4, 1996, now U.S. Pat. No. 5,964,581,which application is a divisional of Ser. No. 08/309,601, filed on Sep.20, 1994, now U.S. Pat. No. 5,711,165, which application is acontinuation of Ser. No. 07/793,119, filed on Nov. 18, 1991, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refrigeration cycle and refrigerantcompressor, and it relates to, in particular, arefrigeration-cycle-constituting material system comprising arefrigerating machine oil composition suitable for a flon typerefrigerant containing no chlorine and having a critical temperature of40° C. or higher, for example, flon 134 a, and electrical insulatingmaterials and a drying agent which are hardly deteriorated by therefrigerating machine oil composition.

2. Prior Art

In recent years, chlorine-containing flons (chlorofluorocarbons,abbreviated as CFC) have been included in the list of compounds underregulation in use, all over the world because of the problems ofenvironmental pollution, in particular, the ozone depletion and theglobal warming.

All of flons included in the list of compounds under regulation in useare chlorine-containing flons such as flon 11, flon 12, flon 113, flon114, flon 115, etc. Flon 12 which has been exclusively used as arefrigerant in refrigerating apparatus such as refrigerators,dehumidifiers, etc., has also been included in the list.

Therefore, a refrigerant usable in place of flon 12 is required.Hydrofluorocarbon (HFC) having a low reactivity with ozone and a shortdecomposition period in the air has recently been noted as a substituterefrigerant. Flon 134 a (1,1,1-tetrafluoroethane, CH₂FCF₃) is a typicalexample of such a refrigerant. In detail, when the ozone depletionpotential (ODP) of flon 12 (dichlorodifluoromethane CCl₂F₂) is taken as1, that of flon 134 a is zero. When the global warming potential (GWP)of flon 12 is taken as 1, that of flon 134 a is 0.3 or less. Flon 134 ais noncombustible and similar to flon 12 in thermal properties such astemperature-pressure characteristics. Therefore, flon 134 a has beensaid to be advantageous in that it can be put into practical use withoutgreatly changing the structures of refrigerating apparatus such asrefrigerators and dehumidifiers and refrigerant compressors in whichflon 12 has heretofore been used.

Flon 134 a, however, has a unique chemical structure and hence verycharacteristic properties. Therefore, it has a very poor compatibilitywith refrigerating machine oils such as mineral oils and alkylbenzeneoils which have been used in conventional refrigeration system usingflon 12, and hence it cannot be put into practical use at all. Inaddition, the suitability including the improving effect on thelubrication and the resistance to frictional wear of the slidingportions of compression mechanical parts, the influence on electricalinsulating materials, the influence on drying agents, etc. is a problem,and there has been an eager desire for the development of a novelmaterial system constituting a compressor and a refrigerating apparatus.

Therefore, before referring to the problem of the miscibility of arefrigerant with a refrigerating machine oil, conventional refrigerantcompressor and refrigeration apparatus which use a flon type refrigerantare first explained with reference to FIG. 7 to FIG. 9.

FIG. 7 is a vertical cross-sectional view of the principal part of aconventional closed rotary compressor. FIG. 8 is a cross-sectional viewfor explaining the displacement volume of the compressor section of thecompressor. FIG. 9 is a diagram showing the structure of an ordinaryrefrigeration cycle.

In FIG. 7, numeral 1 shows a case used both as a closed container and asa oil pan. In the case 1, an electric motor section 22 and a compressorsection 23 are accommodated.

The electric motor 22 is composed of a stator 19 and a rotor 20, and arotating shaft 4A made of cast iron is fitted in the rotor 20. Therotating shaft 4A has an eccentric portion 3 and an shaft hole 17 isformed in hollow form on the one side of the eccentric portion 3.

The core wire of the winding wire portion 19 a of the stator 19 iscoated with an ester imide film, and an electrical insulating film of apolyethylene terephthalate is inserted between the core portion and thewinding wire portion of the stator. The rotor 4A has a surface finishedby grinding.

The compressor 23 has as its chief mechanism components a cylinder 2made of an iron-based sintered product; a roller 7 made of cast ironwhich is fitted in the eccentric portion 3 of the rotating shaft 4A andeccentrically rotated along the inside of the cylinder 2; a high-speedsteel vane which is reciprocated in the groove 8 of the cylinder 2 whileone side of the vane is in contact with the roller 7 and the other sideis pushed by a spring 9; and a main bearing 5 and a sub-bearing 6 whichare made of cast iron or an iron-based sintered product, are provided onboth ends of the cylinder, and serve both as bearings for the rotaryshaft 4A and as the side wall of the cylinder 2.

The sub-bearing 6 has a discharge valve 27, and a discharge cover 25 isattached thereto so as to form a silencer 28. The main bearing 5, thecylinder 2 and the sub-bearing 6 are fastened with a bolt 21.

A pump chamber 12 is composed of a space and parts surrounding thespace, i.e., the back of the vane 10, the groove 8 of the cylinder 2,the main bearing 5 and the sub-bearing 6.

The main bearing 5 has a suction piece 14 which can suck a naphthenetype or alkylbenzene type refrigerating machine oil 13A in which arefrigerant flon gas stored in the bottom of the case 1 has beendissolved, into the pump chamber 12. The sub-bearing 6 has a dischargeport 16 which can discharge the refrigerating machine oil 13A to an oiltube 15 from the pump chamber 12. The oil tube 15 is designed to be ableto supply the refrigerating machine oil 13A to the shaft hole 17 of therotating shaft 4A and then to predetermined sliding portions from theshaft hole 17 through a branch opening 18.

The action of the rotary compressor thus composed is explained belowwith reference to FIGS. 7 and 8. When the compressor is operated torotate the rotating shaft 4A made of cast iron, a roller 7 made oftempered cast iron is rotated with the rotation of rotating shaft 4A,and the high-speed steel vane 10 is reciprocated in the groove 8 of thecylinder 2 made of cast iron or a iron-based sintered product while thevane 10 is pushed by the spring 9 and its end is in contact with theroller 7. Thus, the vane 10 compresses a refrigerant (flon 12) which hasflown in through a refrigerant suction opening (not shown), and therefrigerant is discharged outside the compressor from a discharge pipe29 through a refrigerant discharge opening 24. The winding wire portion19 a and the electrical insulating film (not shown) of the stator 9 areimmersed in the refrigerating machine oil containing flon dissolvedtherein, or they are exposed to circumstances of spraying with mist ofthe refrigerant oil.

In the case of a combination of a conventional refrigerating machine oilconsisting of a mineral oil or an alkylbenzene and flon 12, flon 12 iscompletely miscible with the refrigerating machine oil in all useranges, so that it has been not necessary at all to care about thevarious problems concerning the miscibility of flon 134 a with arefrigerating machine oil which are hereinafter described in detail,namely, the separation into two layers between the refrigerating machineoil and the refrigerant in a compressor, and the residence of therefrigerating machine oil in a heat exchanger. However, in the case offluorohydrocarbon type refrigerants containing no chlorine which haveunique characteristics, for example, flon 134 a, the miscibility of therefrigerant with a refrigerating machine oil is the most serious problemin practice because there is no practical refrigerating machine oilwhich can easily dissolve the refrigerant.

In general, for improving the performance characteristics of acompressor, namely, the coefficient of performance (COP) which indicatesthe energy efficiency, it has been necessary to minimize the mechanicalloss of the compressor and maximize its volumetric efficiency.

The mechanical loss of a refrigerant compressor mainly includes thefriction loss at the journal bearing and thrust bearing in themechanical part and the power for agitating oil. In general, it has beensaid that the best means is to minimize the value of the coefficient offriction (μ) defined by the following equation on the basis of thehydrodynamic lubrication theory of a journal bearing:

μ=2π²(D/C)ηN/P  (9)

wherein

N: revolution rate,

P: pressure on surface,

η: viscosity,

D: diameter of shaft,

C: diametral clearance.

This fact indicates that in a refrigerant compressor operated underhydrodynamic lubrication conditions, not only the structural factorsregarding dimensions and shapes but also the actual viscosity of arefrigerating machine oil containing flon disolved therein which is afactor influenced by operation circumstances, have a close relationshipto the mechanical loss of the compressure.

On the other hand, for keeping the volumetric efficiency highest, it isnecessary that in a mechanical chamber for compressing a refrigerantgas, the leakage of the refrigerant gas from the high pressure side tothe low pressure side should be prevented by carrying out sealingbetween parts which works to compress the refrigerant gas. It should benoted that also in this case, the actual viscosity of a refrigeratingmachine oil containing the refrigerant dissolved therein has animportant function.

As described above, in a refrigerant compressor heretofore used by theuse of flon 12 and a refrigerating apparatus using the refrigerantcompressor, it is important for the improvement of performancecharacteristics of the compressor to optimize the actual viscosity of arefrigerating machine oil containing the refrigerant dissolved therein,at a rated operation point under usual operation conditions.

A refrigerating apparatus such as a refrigerator or a dehumidifier isoperated, though in rare cases, in a high-temperature circumstance muchmore severe than usual operation conditions. In this case, thelubrication in the apparatus gets into a so-called boundary lubricationregion in which a lubricating oil layer is thined, so that the metalsurfaces of sliding portions of a bearing are brought into contact witheach other. Consequently, the coefficient of friction is increased atonce, resulting in heat generation. Therefore, scoring orseizing-and-adhesion phenomenon occurs between the bearing and arotating shaft and deteriorates the reliability of a refrigerantcompressor. Therefore, some consideration is needed for preventing afatal problem from occurring even under boundary lubrication conditions.In a conventional refrigerant compressor using flon 12, chlorine in flon12 acts effectively as an extreme pressure agent. In detail, whenscoring or seizing-and-adhesion phenomenon takes place between a bearingand a rotating shaft, the refrigerant flon 12 dissolved in arefrigerating machine oil as bearing-lubricating oil is decomposed byfrictional heat generated by the scoring or the phenomenon, andchlorine, i.e., the decomposition product, reacts with iron on thesurface of the bearing to form iron chloride which acts as a lubricant.

As described above, in the case of a refrigerating apparatus using ahigh-pressure vessel type rotary compressor, for example, arefrigerator, a refrigerant compressor and a refrigerating apparatuswhich satisfy the operation conditions at an ambient temperature of 30°C. described below are satisfactory in the coefficient of performanceindicating energy efficiency and the reliability of a product, and mostproducts have been used in such ranges. The discharge pressure of thecompressor: about 10 kg/cm²abs, oil temperature: about 100° C.,refrigerating machine oil: an alkylbenzene oil or a mineral oil having aviscosity at 40° C. of 56 cSt and a viscosity at 100° C. of 6 cSt, theactual viscosity of which becomes 1 to 4 cst.

On the other hand, in the case of a refrigerating apparatus using alow-pressure vessel type reciprocating compressor (the explanation ofthe structure and operation is omitted), for example, a refrigerator,there have been used a refrigerant compressor and a refrigeratingapparatus which satisfy the following operation conditions at an ambienttemperature of 30° C.; the suction pressure of the compressor: about 1.6kg/cm² abs, oil temperature: 85° C., refrigerating machine oil: amineral oil having a viscosity at 40° C. of 8 to 15 cSt and a viscosityat 100° C. of 1.8 to 4.2 cSt, the actual viscosity of which becomes 2 to6 cSt.

Next, a fundamental refrigeration cycle provided with a refrigerantcompressor which thus sucks, compresses and then discharge a flon typerefrigerant, is explained below with reference to FIG. 9.

As shown in FIG. 9, a compressor 40 compresses a low-temperature,low-pressure refrigerant gas, discharges the resulting high-temperature,high-pressure refrigerant gas and send the same to a condenser 41. Therefrigerant gas sent to the condenser 41 becomes a high-temperature,high-pressure refrigerant fluid while releasing its heat to the air, andthen it is sent to an expansion mechanism (e.g. an expansion valve or acapillary tube) 42 while being freed from water by a dryer 45. Thehigh-temperature, high-pressure refrigerant fluid which passes theexpansion mechanism becomes low-temperature, low-pressure wet vaporowing to squeezing effect and is sent to an evaporator 43. Therefrigerant introduced into the evaporator 43 is evaporated whileabsorbing heat from the surroundings, and the low-temperature,low-pressure gas which has come out of the evaporator 43 is sucked intothe condenser 40. Thereafter, the above cycle is repeated.

As the frigerant, flon 12 has heretofore been used. However, theemployment of flon 12 is under regulations, as described above. Theemployment of flon 134 a in place of flon 12 involves many problemsbecause conventional mineral oil type or alkylbenzene type refrigeratingmachine oils for flon 12 are very poor in miscibility with flon 134 a.Therefore, refrigerating machine oils having a good miscibility withflon 134 a have been vigorously developed and various refrigeratingmachine oils have been proposed. As typical examples of suchrefrigerating machine oils, there are known the compounds having etherlinkages exemplified below.

For example, Japanese Patent Application Kokai No. 1-259093 discloses “arefrigerating machine oil for a flon compressor” which comprises as baseoil a propylene glycol monoether represented by the general formula:

wherein R is an alkyl group having 1 to 8 carbon atoms, and n is aninteger of 4 to 19; Japanese Patent Application Kokai No. 1-259094discloses a diether type compound obtained by etherifying one end ofpropylene glycol which is represented by the general formula:

wherein each of R₁ an R₂ is an alkyl group having 1 to 8 carbon atoms,and n is an integer (average molecular weight: 300 to 600); and JapanesePatent Application Kokai No. 1-259095 discloses a monoether typecompound which is a copolymer of propylene glycol and ethylene glycoland is represented by the general formula:

wherein R is an alkyl group having 1 to 14 carbon atoms, and m and n areintegers, the ratio m:n being 6:4 to 1:9 (average molecular weight: 300to 2,000).

The difference of these polyalkylene glycols from conventional mineraloils and alkylbenzene oils have been reported as follows. By theintroduction of ether linkages into the molecule, the affinity for flon134 a is enhanced to improve the miscibility with flon 134 a greatly,refrigerant lubrication due to the phenomenon of separation into twolayers (a phenomenon that the refrigerant and the refrigerating machineoil are insoluble in each other and separate; hereinafter referred tomerely as “two-layer separation”) in the sliding portions of acompressor can be prevented, the return of the oil to the compressorwhich is induced by residence phenomenon due to the adhesion of the oilto the inner wall of a heat exchanger can be suppressed, and there canbe solved the problems concerning the reliability of the compressor anda refrigerating apparatus, for example, seizing and scoring in thesliding portions of the compressor.

Such compounds thus containing a large number of ether linkages (C—O—C),however, are disadvantageous in that,

(1) they have a saturation water absorption rate is high (they tend toabsorb water).

(2) they have a low volume resistivity.

(3) they have a low oxidation stability, so that the total acid value isapt to be increased.

Therefore, the compounds have been not suitable for refrigerantcompressors and refrigerating apparatus in which a hermetic motor isused as an electric motor. That is, although the compounds have animproved miscibility with the refrigerant, they are disadvantageous inthat they attack the insulating materials of the motor to deterioratethe electrical insulating characteristics. In all of the abovecompounds, the end group having an ether linkage is capped withhydrogen, and the hydrogen further increases the hygroscopicity.Therefore, it has been proposed to replace the hydrogen by an estergroup to obtain a refrigerating machine oil represented by the followingformula (see Japanese Patent Application Kokai No. 2-132178):

wherein R is a hydrocarbon group, R¹ is an alkylene R² is an alkylgroup, and n is an integer which is such that the viscosity of thiscompound becomes 10 to 300 (at 40° C.).

However, the improved miscibility with the refrigerant of this compoundis also brought about by a large number of ether linkages in themolecule, like that of the above compounds, and hence this compoundinvolves the same problems as in the case of the above compounds.

Thus, the compounds having ether linkages tend to absorb water becauseof the above problem (1), and the compounds themselves are hydrolyzed bythe water to become unstable. Furthermore, the water freezes, chokes thecapillary of a refrigeration cycle, and disturbs the pressure balance.The volume resistivity of the compounds is low as described as theproblem (2), so that the electrical insulating properties aredeteriorated. When the total acid value is increased as described as theproblem (3), the compounds are hydrolyzed to become unstable.

As described above, flon 134 a which is used as a substitute refrigerantfor conventional refrigerant flon 12 involves the following fatalproblem. Because of its unique molecular structure, flon 134 a has a lowaffinity for mineral oil type and alkylbenzene oil type refrigeratingmachine oils which have heretofore been used, and hence it lacksmiscibility with the refrigerating machine oils which is essential in arefrigerant compressor and a refrigerating apparatus.

Attempts have been made to improve the miscibility, but have beenaccompanied with, for example, the deterioration of the electricalinsulating properties, the water problem, and the unstability problems,such as the hydrolysis and the decomposition of the compound by an acid.Each problem is described below in more detail.

SUMMARY OF THE INVENTION

(1) A refrigerating machine oil having a bad miscibility cannot be putinto practical use in a refrigerant compressor and a refrigeratingapparatus from the viewpoint of performance characteristics andreliability, as described below.

In general, when the solubility of a refrigerating machine oil in arefrigerant is low, oil discharged from a compressor is separated in aheat exchanger and the oil component adheres to the wall surface toremain, so that the amount of oil which returns to the compressor isdecreased. Consequently, the oil surface in the compressor is loweredand a so-called oil drying-up phenomenon takes place, so that the oilinglevel is lowered.

When a compressor is exposed to a low-temperature circumstance in arefrigerating apparatus enclosing a large amount of a refrigerant, thefollowing trouble is caused. In a so-called lying-idle state in whichliquid refrigerant is present preferentially in the bottom of thecompressor, low-viscosity liquid refrigerant which is present in thebottom as a result of two-layer separation is supplied to the slidingsurface of a rotating shaft, so that the assurance of a lubricating oilfilm becomes difficult, resulting in damage to the compressor.

On the other hand, as to the refrigerating apparatus, a refrigeratingmachine oil which has separated adheres to the inner wall of anevaporator having a low temperature, to form a heat-insulating layer,and therefore it inhibits the heat-transferring capability seriously.Moreover, when this refrigerating machine oil of wax form chokes anexpansion mechanism (a capillary tube) or a piping, the amount of therefrigerant circulated is greatly decreased, resulting in a loweredcooling power. As to the compressor, the pressure of sucked gas islowered and the pressure of discharged gas is increased. Therefore, theheat deterioration of the refrigerating machine oil and damage tobearings are caused, so that the long-term reliability of therefrigerant compressor and the refrigerating apparatus is greatlydeteriorated.

Accordingly, a first object of the present invention is to solve suchconventional problems and provide a refrigerating apparatus and arefrigerant compressor which are provided with a refrigerating machineoil which is highly miscible with and hence suitable for flon typerefrigerants containing no chlorine a typical example of which is flon134 a. More specifically, the present invention is fundamentallyintended to make improvements with respect to, for example, (1) waterabsorption properties, (2) volume resistivity, and (3) oxidativedeterioration, and seek for a novel refrigerating machine oilcomposition which is miscible with flon 134 a under all operationconditions of a refrigerant compressor and a refrigerating apparatus. Itis also intended to provide a refrigeration system having excellentperformance characteristics, efficiency and reliability in refrigeratingapparatus and refrigerant compressors which are different in purposes,by developing at least the following two refrigeration oils: arefrigeration oil for moderate-temperature refrigerating apparatus suchas dehumidifiers which achieves a first aim, i.e., attainment of acritical solution temperature of 0° C. or lower; and a refrigeration oilfor low-temperature refrigerating apparatus such as refrigerators whichachieves a second aim, i.e., attainment of a critical temperature of−30° C. or lower.

(2) In the long run, it is beneficial to the prevention of globalwarming (GWP) to enhance the coefficient of performance (COP) (whichindicates the energy efficiency, i.e., the ratio of the cooling power ofa refrigerant compressor to an input) under usual use conditions underwhich refrigerant compressors and refrigerating apparatus are usuallyoperated.

For reducing the input to a compressor in order to improve theperformance characteristics of the compressor, it is necessary toreducve the coefficient of friction on the basis of the hydrodynamiclubrication theory of coaxial bearing. For the reduction, it isnecessary to measure the solubility of flon 134 a in the refrigeratingmachine oil used in the present invention and thereby determine theoptimum value of the actual viscosity of the oil used in the compressor.When the actual viscosity is thus optimized, the coefficient of frictionof a bearing becomes minimum and the coefficient of performance of thecompressor and a refrigerating apparatus using the compressor becomesmaximum.

Therefore, a second object of the present invention is to attain highperformance characteristics and a high reliability by specifying aviscosity range of the refrigerating machine oil which is most suitablefor a refrigerating apparatus using a high-pressure vessel type rotarycompressor or a low-pressure vessel type reciprocating compressor, onthe basis of the above bearing theory.

(3) However, although very rarely in practice, there is carried out anextremely severe operation such as operation in a high-temperaturecircumstance or overload operation which are more severe than expectedby a designer. Also in this case, a sufficient reliability should beassured.

In a compressor using flon 134 a, scoring or seizing of the slidingportion of a bearing of the compressor tends to take place more oftenthan in a compressor using a conventional refrigerant flon 12, in aso-called boundary lubrication region (in which contact between metalsurfaces occurs) beyond the hydrodynamic lubrication region of a coaxialbearing.

When contact between metal surfaces takes place in the sliding portionof a bearing, flon 12 dissolved in an oil is decomposed to form aconversion coating of iron chloride on an iron-based sliding frictionalsurface. This iron chloride acts as an extreme pressure agent tosuppress the adhesion and seizing.

On the other hand, since flon 134 a is a refrigerant containing nochlorine, chlorine cannot possibly be supplied to a compressor usingflon 134 a. Therefore, unlike flon 12, flon 134 a is hardly expected tohave the above action as extreme pressure agent.

Accordingly, a third object of the present invention is to provide arefrigerating apparatus and a refrigerant compressor in which by using aflon type refrigerant containing no chlorine represented by flon 134 aand a refrigerating machine oil containing an extreme pressure agent,the prevention of scoring and seizing of the sliding portions and theassurance of sufficient reliability can be achieved even when the oilruns out in the sliding bearing of the compressor and extremely severeoperation is carried out.

(4) A fourth object of the present invention is to provide a refrigerantcompressor and a refrigerating apparatus which use a compositioncomprising a flon type refrigerant containing no chlorine represented byflon 134 a and a refrigerating machine oil, and have an electricalinsulating system wherein electrical insulating materials such as anelectrical insulating film and an insulation-coated winding wire whichconstitute an electric motor section have a sufficient long-termreliability.

(5) Flon 134 a has a high water absorption rate and refrigeratingmachine oils miscible with flon 134 a are relatively hydrophilic thoughfairly improved. Therefore, both of them tend to carry water into arefrigeration cycle. Water in a refrigerating apparatus is frozen in anevaporator on the low-temperature side and chokes a pipe having a smalldiameter, such as a capillary tube to lower the refrigeratingcapability. Furthermore, in the long run, the refrigerating machine oil,the refrigerant, electrical insulating materials, etc. undergohydrolysis reaction, so that minus characteristics are brought about,for example, the production of an acidic substance and a lowering of themechanical strength are induced.

Accordingly, a fifth object of the present invention is to provide arefrigerating apparatus in which a flon type refrigerant containing nochlorine represented by flon 134 a and a refrigerating machine oilcoexists, and which has a dryer packed with a drying agent effective inimproving the reliability of the refrigerating apparatus by separatingand adsorbing only water without absorbing the refrigerant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a two-layer separation temperature whichillustrates the miscibility of flon 134 a with each refrigeratingmachine oil.

FIG. 2 is a graph showing a relationship between the amount of waterdissolved in each of various refrigerating machine oils and its volumeresistivity.

FIG. 3 is a graph showing a relationship between the atual viscosity ofeach refrigerating machine oil and the coefficient of performance duringrated operation of a high-pressure vessel type rotary compressor.

FIG. 4 is a graph showing a relationship between the actual viscosityand the coefficient of performance during rated operation of alow-pressure vessel type reciprocating compressor.

FIG. 5 is a graph showing a relationship between FALEX test using aniron-based frictional sliding surface and a high-pressure atmospherefriction test using an oil containing flon 134 a dissolved therein.

FIG. 6 is a graph showing the abration loss caused by a FALEX test.

FIG. 7 is a vertical cross-sectional view of the principal part of aclosed rotary compressor.

FIG. 8 is a vertical cross-sectional view of the principal part of thecompression mechanical part of a rotary compressor.

FIG. 9 is a diagram showing the structure of the refrigeration cycle ofa refrigerating apparatus.

PREFERRED EMBODIMENT OF THE INVENTION

1. The above first object of the present invention can be achieved by arefrigerating apparatus comprising a refrigeration cycle comprising atleast a compressor, condenser, dryer, expansion mechanism andevaporator, a refrigerant composed mainly of a fluorocarbon typerefrigerant containing no chlorine and having a critical temperature of40° C. or higher, and a refrigerating machine oil comprising as base oilan ester oil of one or more fatty acids which contains at least twoether linkages

in the molecule and has a viscosity at 40° C. of 2 to 70 cSt and aviscosity at 100° C. of 1 to 9 cSt.

As described above, it is absolutely necessary for the ester oil to bean ester of one or more fatty acids which contains at least two esterlinkages in the molecule. Ester oils of one or more fatty acids whichhave one ester linkage have a bad miscibility with the refrigerant andhence cannot be used. The usable ester oil of one or more fatty acidscan be obtained by the esterification reaction of an alcohol with one ormore fatty acids. As the alcohol, a polyhydric alcohol is preferable. Asthe fatty acids, those having 1 to 6 carbon atoms are preferable. Thefatty acids may be either monobasic or polybasic. The ester oils includehindered ester oils and complex ester oils. From the viewpoint of themiscibility with the refrigerant, ester oils having a branched-chainstructure tend to be preferable to ester oils having a straight-chainstructure. Examples of practical ester oils of one or more fatty acidsare given below by the general formulas (1) to (5).

The ester oils represented by the formulas (1) to (4) are hindered esteroils, and the ester oils represented by the formula (5) are complexester oils.

These ester oils may be used singly or in combination of two or morethereof. The refrigerating machine oil comprise at least 50 wt % ofthese ester oils as base oil, and the balance may be made up by otherwell-known refrigerating machine oils.

(R₁CH₂)₂C(CH₂OCOR₂)₂  (1)

(examples of esters of neopentyl glycol (abbreviated as NPG) typealcohols which contain two ester linkages in the molecule).

R₁CH₂C(CH₂OCOR₂)₃  (2)

(examples of esters of trimethylolalkylpropanes (abbreviated as TMP)which contain three ester linkages in the molecule).

C(CH₂OCOR₂)₄  (3)

(examples of esters of pentaerythritol (abbreviated as PET) whichcontain 4 ester linkages in the molecule).

(R₂COOCH₂)₃CCH₂OCH₂C(CH₂OCOR₂)₃  (4)

(examples of esters of dipentaerythritol (abbreviated as DPET) whichcontain 6 ester linkages in the molecule).

(examples of complex esters containing 4 or more ester linkages in themolecule).

In the above general formulas, R₁ is H or an alkyl group having 1 to 3carbon atoms, R₂ is a straight or branched-chain alkyl group having 5 to12 carbon atoms, R₃ is an alkyl group having 1 to 3 carbon atoms, R₃ isan alkyl group having 1 to 3 carbon atoms, and n is an integer of 0 to5.

The esters represented by the above general formulas (1) to (4) areesters of polyhydric alcohols and monocarboxylic acids. As such esters,esters having a desired viscosity grade can be obtained by optionallychoosing a combination of the alcohol and one or a plurality of themonocarboxylic acids and proportions of these components.

As the complex esters represented by the general formula (5), estershaving a high viscosity and a wide critical solution temperature rangecan be obtained by selecting the chemical structure of the centraldibasic acid (dicarboxylic acid) component from various chemicalstructures derived from succinic acid (n=2), glutaric acid (abbreviatedas Glut), adipic acid (abbreviated as AZP), pimelic acid, suberic acid,azelaic acid, and sebacic acid (n=8), selecting the polyhydric alcoholcomponent and the terminal monocarboxylic acid component from variouscompounds, and varying the blending proportions (molar fraction).

The monocarboxylic acids represented by the formula R₂COOH may bestraight- or branched-chain ones. The latter includes 2-ethylhexanoicacid (2EH), 2-methylhexanoic acid (i-C₇), 3,5,5-trimethylhexanoic acid,3,5-dimethylhexanoic acid (i-C₈), 2-methylheptanoic acid. Themonocarboxylic acids may be used singly or in combination of two or morethereof.

The base oil of the refrigerating machine oil is prepared by adjustingthe viscosity by using such hindered ester oils and complex ester singlyor in combination of two or more thereof.

The refrigerant composed mainly of a fluorocarbon type refrigerantcontaining no chlorine and having a critical temperature of 40° C. orhigher which is used in the present invention includeshydrofluorocarbons and fluorocarbons. Specific examples of thehydrofluorocarbons are difluoromethane (R32), pentafluoroethane (R125),1,1,2,2-tetrafluoroethane (R134), 1,1,1,2-tetrafluoroethane (R134 a),1,1,2-trifluoroethane (R143), 1,1,1-trifluoroethane (R143 a),1,1-difluoroethane (R152 a) and monofluoroethane (R161). Specificexamples of the fluorocarbons are hexafluoropropane (C216) andoctafluorocyclobutane (C318). Of these, 1,1,2,2-tetrafluoroethane(R134), 1,1,1,2-tetrafluoroethane (R134 a), 1,1,2-trifluoroethane(R143), 1,1,1-trifluoroethane (R143 a) and hexafluoropropane (C216) havea boiling point close to that of a conventional refrigerant,dichlorodifluoromethane (R12), and are preferable as substituterefrigerants. The above-exemplified hydrofluorocarbon or fluorocarbontype refrigerants can be used singly or as a mixture thereof.

The reason for the adjustment of critical temperature of the refrigerantto 40° C. or higher is that there was required a refrigerating apparatusin which the condensation temperature in a condenser was 40° C.

1) The above second object of the present invention is, for one thing,achieved by a high-pressure vessel type refrigerant compressor used in arefrigeration cycle that comprises a closed vessel stored with arefrigerating machine oil which accommodates a motor composed of a rotorand a stator, a rotating shaft fitted in the rotor, and a compressorsection connected to the motor through the rotating shaft, and in whicha high-pressure refrigerant gas discharged from the compressor sectionresides, said refrigerant being composed mainly of a fluorocarbon typerefrigerant containing no chlorine and having a critical temperature of40° C. or higher, and said refrigerating machine oil comprising as baseoil an ester oil of one or more fatty acids which contains at least twoester linkages

in the molecule and has a viscosity at 40° C. of 2 to 70 cSt and aviscosity at 100° C. of 1 to 9 cSt.

The constitution of the ester oil of one or more fatty acids whichcontains at least two ester linkages in the molecule is as describedabove in detail.

In a high-pressure vessel type rotary compressor, for example, ispreviously enclosed the aforesaid refrigerating machine oil having aviscosity at 40° C. of 2 to 70 cSt, preferably 5.0 to 32 cSt, so thatthe actual viscosity (at a gas pressure of 9 to 11 kg/cm² abs and an oiltemperature of about 100° C.) of the oil which contains flon 134 adissolved therein may be 1.0 to 4.0 cSt.

2) In addition, the above second object of the present invention isachieved by a low-pressure vessel type refrigerant compressor thatcomprises a closed vessel stored with a refrigerating machine oil whichaccommodates a motor composed of a rotor and a stator, a rotating shaftfitted in the rotor, and a compressor section connected to the motorthrough the rotating shaft, and from which a high-pressure refrigerantgas discharged from the compressor section is directly exhausted, saidrefrigerant being composed mainly of a fluorocarbon type refrigerantcontaining no chlorine and having a critical temperature of 40° C. orhigher, and said refrigerating machine oil comprising as base oil anester of one or more fatty acids which contains at least two esterlinkages

in the molecule and has a viscosity at 40° C. of 2 to 70 cSt and aviscosity at 100° C. of 1 to 9 cSt.

The constitution of the ester oils of one or more fatty acids whichcontains at least two ester linkages in the molecule is as describedabove.

In a low-pressure vessel type reciprocating compressor, for example, ispreviously enclosed the aforesaid refrigerating machine oil having aviscosity at 40° C. of 5.0 to 15 cSt and a viscosity at 100° C. of 2.0to 4.0 cSt, so that the actual viscosity (at a sucked gas pressure of1.0 to 2.0 kg/cm abs and an oil temperature of 85° C.) of the oil whichcontains flon 134 a dissolved therein may be 2.0 to 4.5 cSt.

3) The above third object can be achieved by adding an extreme pressureagent to the aforesaid refrigerating machine oil.

The extreme pressure agent serves as an abration-preventing agent insliding portions and includes, for example, alkylpolyoxyalkylenephosphate esters represented by the general formulas (6) and (7) anddialkyl phosphate esters represented by the general formula (8):

wherein R₄ is an alkyl group having 1 to 8 carbon atoms, and R₅ is H oran alkyl group having 1 to 3 carbon (molecular weight: 400 to 700).

wherein R₆ is an alkyl group having 8 to 16 carbon atoms.

These phosphoric esters may be added singly or in combination of two ormore thereof. The practical amount of the phosphoric esters added to therefrigerating machine oil is 0.05 to 10 wt %.

It is also effective to add an acid-capturing agent, antioxidant,defoaming agent, etc. together with the extreme pressure agent (theabrasion-preventing agent).

When an acid component is present in the refrigerating machine oil, theester oil is decomposed by the acid component to become unstable.Therefore, the acid-capturing agent is added for removing the acidcomponent. For example, compounds such as epoxy compounds reactive withacids are preferable as the acids-capturing agent. Particularlypreferable examples of the acid-capturing agent are compounds having anepoxy group and an ether linkage, for example, diglycidyl ethercompounds such as polyalkylene glycol diglycidyl ethers; monoglycidylether compounds such as phenyl glycidyl ether; and aliphatic cyclicepoxy compounds. The reason is that the epoxy group of such a compoundcaptures an acid and that the ether linkage contributes to theimprovement of the miscibility of the refrigerating machine oil with therefrigerant to a certain extent.

The other additives described above are, for example, chlorine-capturingagents for preventing the influence of residues of, for instance, achlorine-containing detergent used for producing the compressor or therefrigerating apparatus, additives for preventing oxidativedeterioration during the circulation and storage of the oil, andadditives for preventing foaming. These additives may be selected fromthose used in the conventional general techniques and are not criticalin the present invention.

4) For achieving the fourth object, the insulating film constituting anelectric motor section and the insulation-coated winding wire which aredescribed below are used in a refrigerating apparatus and a refrigerantcompressor which simultaneously use a flon type refrigerant containingno chlorine represented by flon 134 a and a refrigerating machine oilcomprising as base oil the above-exemplified ester oil of one or morefatty acids. As the insulating film, there is used a crystallineplastics film having a glass transition temperature of 50° C. or higher,or a composite film obtained by coating a film having a low glasstransition temperature with a resin layer having a high glass transitiontemperature. As the insulation-coated winding wire, there is used anenameled wire having the enamel coating of a glass transitiontemperature of 120° C. or higher, or an enameled wire having a compositecoating consisting of a lower layer having a low glass transitiontemperature and a upper layer having a high glass transitiontemperature.

As the insulating film, for practical purposes, it is preferable to useat least one kind of insulating film selected from the group consistingof films of polyethylene terephthalates, polybutylene terephthalates,polypenylene sulfides, polyether ether ketones, polyethylenenaphthalates, polyamide-imides and polyimides. As an enamel coating, itis preferable to use at least one kind of insulating layer selected fromthe group consisting of insulating layers of polyester imides,polyamides and polyamide-imides.

5) For achieving the fifth object, a synthetic zeolite composed of acomposite salt consisting of alkali metal silicates and alkali metalaluminates which has a pore diameter of 3.3 angstrom or less and acarbon dioxide gas absorption capacity (at 25° C. and at a partialpressure of carbon dioxide gas of 250 mmHg) of 1.0% or less, is used asa drying agent to be packed into the dryer, in the aforesaidrefrigerating apparatus which simultaneously uses a flon typerefrigerant containing no chlorine represented by flon 134 a and arefrigerating machine oil comprising as base oil the above-exemplifiedester oil of one or more fatty acids.

In a refrigerating apparatus comprising at least a compressor,condenser, expansion mechanism and evaporator, and using a flon typerefrigerant containing no chlorine represented by flon 134 a, therefrigerating machine oil according to the present invention whichcomprises at least one ester selected from the group consisting ofhindered or complex esters containing two or more ester linkages in themolecule, and has a viscosity at 40° C. of 2 to 70 cSt, preferably 5 to32 cSt, and a viscosity at 100° C. of 1 to 9 cst, preferably 2 to 6 cSt,has a good miscibility with the refrigerant in the whole temperatureranges of the parts used in the refrigerating apparatus. Therefore,there is no two-layer separation between the refrigerant and therefrigerating machine oil. Accordingly, no two-layer separation ispresent in the oil-storing space in the compressor, so that the supplyof the oil to the sliding portions of hearings is assured, and flon gasdischarged from the compressor is in a liquefied state by the condenser,namely, in a state in which the oil is always dissolved in flon 134 awith a low viscosity in a low-temperature circumstance of −30° C. orlower in the evaporator. Thus, on the whole, the flon gas is in alow-viscosity state, so that the return of the oil to the compressor isimproved.

Therefore, the lowering of oil surface in the compressor is preventedand hence the supply of the oil to the sliding portions of hearings canbe assured. Thus, the problems causing scoring and seizing can besolved.

Furthermore, unlike conventional polyoxyalkylene glycol oils, theaforesaid refrigerating machine oil has a low saturated water-content ofone-tenth or less as large as that of the conventional oils, a largeimproving effect on the stability to oxidative deterioration, and avolume resistivity of 10¹³ Ωcm which is as high as that of an electricalinsulating oil. Therefore, in a refrigerant compressor comprising apressure vessel accommodating a motor section and a refrigeratingapparatus using the refrigerant compressor, the refrigerating machineoil according to the present invention do not separate from flon 134 aand has excellent characteristics with respect to both the performancecharacteristics and reliability of the compressor. Since therefrigerating machine oil has an excellent miscibility also withconventional chlorine-containing flon refrigerants such as flon 12 andflon 22, such conventional chlorine-containing refrigerants can, ifnecessary, be used in place of a portion of flon 134 a in admixture withflon 134 a.

When the refrigerating machine oil according to the present inventionwhich had an oil viscosity at 40° C. of 5 to 32 cSt was enclosed in ahigh-pressure vessel type rotary compressor and the coefficient ofperformance of the compressor was measured, the coefficient ofperformance reached a peak in the case of using the oil which had aviscosity of 15 cSt. When the oil which had a viscosity of 5 to 32 cStwas used, the coefficient of performance was about 1.4 or more whichcorresponds to a value of 0.95 to 0.93 when the coefficient ofperformance in the case of using a conventional combination of a flon 12and an alkylbenzene oil is taken as 1. Such a value indicates that theoil involves no practical problem. The refrigerating machine oilaccording to the present invention which had a viscosity at 40° C. of 56cSt was found to be superior in the coefficient of performance of thecompressor to polyoxypropylene glycol oils. The reason for thissuperiority is as follows. The ester linkages contained in the oilitself undergoes molecular orientation mainly on the surfaces ofiron-based sliding portions of the shaft and bearings of the compressorto improve the lubrication. Moreover, the oil is decreased in actualviscosity owing to its high solubility in flon 134 a, to reduce themechanical loss. These effects are synergistically brought about toimprove the coefficient of performance of the compressor.

On the other hand, in the case of a low-pressure vessel typereciprocating compressor, the amount of flon 134 a dissolved and theactual viscosity vary only in narrow ranges because the compressor isoperated at a low pressure in the vessel of 1 to 2 kg/cm² abs.Therefore, characteristics of a refrigerant and a refrigerating machineoil are hardly dependent on their kinds, and it was found that the oilwhich had a viscosity at 40° C. of 5 to 15 cSt and a viscosity of 100°C. of 2 to 4 cSt was good in reliability and performancecharacteristics.

When the refrigerating machine oil according to the present invention isblended with an adequate amount (0.05 to 10 wt %) of an extreme pressureagent such as a strong primary or secondary phosphoric ester retainingOH groups in the molecule, for example, an alkylpolyoxyalkylenephosphate ester or a dialkyl phosphate ester, the resulting blend canpush away a lubricating oil film having ester linkages undergoingmolecular orientation on the surfaces of iron-based sliding portionsconstituting the shaft and bearings of the compressor, and form astronger chemical adsorption film of the phosphoric ester. Therefore,the blend can further improve the lubrication of the sliding portions toprevent scoring and seizing.

When the lubricating properties of the refrigerating machine oilaccording to the present invention containing the extreme pressure agentwere examined, the critical seizing pressure on surface was greatlyincreased in a FALEX test (a seizing test on the oil) carried outwithout the dissolution of flon 134 a in the oil. In addition, whenthere was measured the abrasion loss of an iron-based sliding member inthe case of employment of the refrigerating machine oil containing theextreme pressure agent which further contained 50% of flon 134 adissolved therein, as simulation of the dissolution of a highconcentration of flon 134 a, the abrasion loss could be reduced toone-fifth or less as large as that caused in the case of the oil whichdid not contain the extreme pressure agent. The suitable range of theamount of the extreme pressure agent added is 0.05 to 10 wt % asdescribed above. The results of the abrasion loss test are as shown inFIG. 6 though specifically described in the examples hereinafter given.As shown in FIG. 6, the reducing effect of the addition of the extremepressure agent on the abrasion loss is remarkable.

Conventional additives such as an acid-capturing agent, antioxidant,defoaming agent, etc. can be blended together with the extreme pressureagent.

Next, there are explained below electrical insulating materials for therefrigerant compressor using flon 134 a together with the refrigeratingmachine oil according to the present invention. As an insulating filmused as electrical insulating material for the motor section, acrystalline plastics film having a glass transition temperature of 50°C. or higher is used. The insulating film includes films of polyethyleneterephthalates, polybutylene terephthalates, polyphenylene sulfides,polyether ether ketones, polyethylene naphthalates, polyamide-imides andolyimides; and composite films obtained by coating a film having a lowglass transition temperature with a resin layer having a high glasstransition temperature. These films are hardly deteriorated in tensilestrength characteristics and electrical insulating characteristics andinvolve no practical problem. This is because the films carry in a muchsmaller amount of water and produce a much smaller amount of an acidthan do conventional polyoxyalkylene glycol oils, and hence are hardlydeteriorated by hydrolysis of the films themselves.

An enamel coating having a glass transition temperature of 120° C. orhigher is used on a magnet wire used in the motor section. The enamelcoating includes, for example, monolayers of polyester imides,polyamides, polyamide-imides and the like, and composite enamel coatingfilms obtained by forming an upper layer having a high glass transitiontemperature on a lower layer having a low glass transition temperature.Like the above-mentioned films, these enamel coatings hardly showdeterioration by hydrolysis, cracking, softening, swelling, a loweringof breakdown voltage, etc. and hence are useful for improving thereliability in practical. In some cases, a self-lubricating agent or anexternal lubricating agent is included in the enamel coating on themagnet wire, for imparting self-lubricating properties to improve theelectrical workability. Fundamentally, the above characteristics of theenamel coating itself before the inclusion are retained.

Lastly, a drying agent packed into the dryer of the refrigeratingapparatus in which flon 134 a and the aforesaid refrigerating machineoil according to the present invention coexist is explained below. Inthis invention, it is preferable to use a synthetic zeolite composed ofa composite salt consisting of alkali metal silicates and alkali metalaluminates which has a pore diameter of 3.3 angstrom or less, a carbondioxide absorption capacity at 25° C. and at a carbon dioxide partialpressure of 250 mmHg of 1.0% or less. As such a synthetic zeolite, XH-9and XH-600 (trade names, mfd. by UNION SHOWA K.K.) can be exemplified.Both of them have a small fluorine ion adsorption. The same syntheticzeolite as above except for having a carbon dioxide gas adsorptioncapacity of 1.5% or more has a fluorine adsorption of as large of 0.24%or more and hence possesses deteriorated adsorption characteristics andbreaking strength as molecular sieves. Moreover, corroded crystaldisintegration product of such a synthetic zeolite chokes the piping ofthe refrigeration cycle or injures the sliding portions of bearings ofthe compressor. When the pore diameter in the present invention isspecified in relation to the above carbon dioxide adsorption capacity inconsideration of such conditions, the troubles described above are notcaused and it becomes possible to compose a highly reliablerefrigerating apparatus.

Examples of the present invention are explained below with reference toFIGS. 1 to 6 and Tables 1 to 4.

EXAMPLES 1 TO 17

These examples show embodiments for achieving the above first object ofthe present invention. In a closed rotary compressor concerned with arefrigeration cycle and a refrigerant compressor, flon 134 a was used asa refrigerant, and as a refrigerating machine oil, there was used eachester oil listed in Table 1 which contained two or more ester groups inthe molecule and had a viscosity at 40° C. of 2 to 70 cSt and aviscosity at 100° C. of 1 to 9 cSt. For comparison, data on conventionalrefrigerating machine oils are also shown in Table 1.

FIG. 1 is a graph showing two-layer separation temperature whichillustrates the miscibility of flon 134 a with each refrigeratingmachine oil. The graph was obtained by enclosing flon 134 a and therefrigerating machine oil in a high-pressure glass vessel, observingvisually the two-layer separation state at each temperature and at eachconcentration of the refrigerating machine oil, and summarizing theobservation results. The axis of abscissa refers to the concentration ofthe oil in flon 134 a, and the axis of ordinate to temperature. Thefirst target value shown in FIG. 1 is a lower critical solutiontemperature necessary for a refrigerating apparatus such as adehumidifier, which has a moderate evaporator temperature (0° C. orlower). The second target value is a lower critical solution temperaturenecessary for a refrigerating apparatus such as a refrigerator, whichhas a low evaporator temperature (−30° C. or lower). Both of theevaporator temperatures are specified values.

From Table 1, it can be seen that SUNISO 4GSD (a trade name, naphthenetype) and Z300A (a trade name, alkylbenzene type) both manufactured byJAPAN SUN OIL Co., Ltd. were not dissolved. A polyalkylene glycol, PAG56(a trade name, mfd. by JAPAN SUN OIL Co., Ltd.) had a lower criticalsolution temperature (shown by L1) of −60° C. and an upper criticalsolution temperature (shown by U1) of 35° C. The ester oils containingtwo or more ester groups in the molecule according to the presentinvention are so excellent in critical solution temperatures that theirlower critical solution temperature (shown by L2) is −70° C. and theirupper critical solution temperature (shown by U2) 70° C. or higher. Thelower critical solution temperatures is an important factor forpractical purposes in the heat exchanger of a refrigerating apparatus,and the upper critical solution temperature is an important factor forpractical purposes in a refrigerant compressor.

FIG. 9 is a diagram showing the structure of the refrigeration cycle ofa refrigerating apparatus. The refrigerating apparatus comprising arefrigerant compressor 40, a condenser 41, a dryer 45, an expansionmechanism 42 and an evaporator 43 was operated by using each of theabove-mentioned refrigerating machine oils together with flon 134 a.Consequently, in the case of SUNISO 4GSD (a naphthenic mineral oil) andZ300A (an alkylbenzene oil) (trade names, mfd. by JAPAN SUN OIL Co.,Ltd.), when the refrigerant was present in a large amount and lay idlein the compressor, a refrigerant layer having a high density and arefrigerating machine oil layer having a low density were present merelyas a lower layer and an upper layer, respectively, owing to two-layerseparation. Therefore, as shown in FIG. 7, i.e., the verticalcross-sectional view showing the principal part of a refrigerantcompressor (an example of closed rotary compressor), oil supply to ashaft 4A, a main bearing 5 and a sub-bearing 6 is carried out by suctionof the refrigerant layer present merely as the lower layer through thesuction opening 14 of a pump. The refrigerant layer has a lowerviscosity than does the refrigerating machine oil. Therefore, when therefrigerant layer is supplied to the bearings, the resulting oil film isthin, so that contact between metal surfaces tends to occur. Inaddition, since the temperature of sliding frictional surfaces rises atonce, the refrigerant was gasified, resulting in more severe conditions.When this phenomenon is repeated, damages due to scoring and seizing arecaused in the shaft and the bearings, so that the performancecharacteristics of the refrigerant compressor are lost.

When the conventional refrigerating machine oil is used in the heatexchanger of the refrigerating apparatus shown in FIG. 9, for example,the evaporator 43 used at 0° to −60° C., the refrigerating machine oilwhich has been discharged together with gas of the refrigerant from thecompressor 40 undergoes two-layer separation in the evaporator 43 andadheres to the inner wall of the piping of the heat exchanger, and thereis caused the residence of the refrigerating machine oil or the heatinsulation of the heat exchanger. Therefore, the conventionalrefrigerating machine oils greatly deteriorate the cooling capability ofthe refrigerating apparatus and are of no practical use. In this point,the polyalkylene glycol listed as Conventional Example 3 in Table 1 isadvantageous because it has a lower critical solution temperature of−60° C. and hence does not undergo two-layer separation in theevaporator 43. But, owing to its upper critical solution temperature of35° C., it completely undergoes two-layer separation because thetemperature of the compressor 40 during operation becomes at least 80°C. As in the case of Conventional Examples 1 and 2, when thepolyalkylene glycol is supplied to the bearings, damages due to scoringand seizing are caused in the shaft and the bearing, so that therefrigerant compressor loses its performance characteristics.

In a refrigerant compressor having a hermetic motor, for example, therotary compressor shown in FIG. 7, a refrigerating machine oil is, ofcourse, required to have characteristics as an electrical insulatingoil.

FIG. 2 shows the relationship between the water absorption and thevolume resistivity of each of the ester oils according to the presentinvention and conventional mineral oil and polyalkylene glycol. Even ina condition in which the water content is controlled to be 500 ppm orless, the polyalkylene glycol as conventional example has a low volumeresistivity of 10¹² Ωcm or less owing to the ether linkages in themolecule and hence is not preferable.

On the other hand, the refrigerating machine oil having ester linkagesintroduced thereinto according to the present invention has a highvolume resistivity (a high insulating capability) of 10¹³ Ωcm or morewhich is in accordance with the standard value of electrical insulatingoil prescribed in JIS C2320. Therefore, it can be sufficiently put topractical use. Although the mineral oil as conventional example has ahigh insulating capability, it has a bad miscibility with flon 134 a andcannot be put to practical use.

Next, the relationship among the kind, chemical structure and lowercritical solution temperature of ester oils suitable for flon 134 a isexplained below in detail with reference to Table 1.

The ester oil containing two or more ester groups in the molecule whichis used in the present invention includes esters of monobasic orpolybasic organic acids and polyhydric alcohols. Typical examples of theester oil are hindered ester oils and complex ester oils which arerepresented by esters of neophentyl glycol, esters of trimethylolpropaneor trimethylolethane, and esters of pentaerythritol. Table 1 shows therelationship amount the name, viscosity and critical solutiontemperatures of typical chemically synthesized products.

TABLE 1 Critical solution Viscosity temperature (° C.) (cSt) U L Samplerefrigerating machine oil 40° C. 100° C. (upper) (lower) Conventional 1Naphthenic mineral oil 55.1 5.9 — >40 Example (SUNISO 4GSD) 2Alkylbenzene oil 60.1 6.0 — >40 (SUNISO Z300A) 3 Propylene glycol 54.010.0 35 −60 monoether (PAG56) Example 1 Note 1 NPG/n-C₈ 4.8 1.7 −29 2NPG/n-C₇ 2.8 1.2 −61 3 NPG/2EH 7.0 2.1 >80 −60 4 NPG/i-C₇ 5.5 1.8 >80−70 5 NPG/i-C₁₁ 14.9 3.8 >80 −40 6 Note 2 TMP/n-C₇ 13.9 3.4 −20 7TMP/n-C₆ 10.8 2.8 −62 8 TMP/i-C₈ 32.2 5.2 −27 9 TMP/2EH 22.0 4.2 −33 10TMP/i-C₇ 14.9 3.4 >80 −60 11 Note 3 PET/n-C₆ 17.5 3.7 −44 12 PET/2EH52.0 6.7 −8 13 PET/i-C₇ 28.0 4.8 −40 14 Note 4 NPG/Glut/n-C₆ 32.65.9 >80 <−75 15 NPG/i-C₇ + 29.5 5.0 >80 −45 AZP/NPG/n-C₁₀ 16AZP/NPG/n-C₁₀ 54.5 7.3 >80 −60 17 Glut/NPG/i-C₆ 56.6 8.6 >80 −60 Note 1NPG: esters of neopentyl glycol, i-C₇:

n-C₇: CH₃(CH₂)₅COOH, i-C₁₁: CH₃(CH₃)CH(CH₂)₇COOH Note 2 TMP: esters oftrimethylolpropane, i-C₈:

n-C₆: CH₃(CH₂)₄COOH Note 3 PTE: esters of pentaerythritol Note 4:complex esters, n-C₁₀: CH₃(CH₂)₈COOH, i-C₆: CH₃(CH₃)CH(CH₂)₂COOH

Of the sample names in Table 1, the names of chemically synthesizedester oils are abbreviated. For example, in the case of NPG/n-C₈, NPG isan abbreviation of neopentyl glycol, n-C₈ is an abbreviation of a normalorganic acid (a straight-chain fatty acid) having 8 carbon atoms, andNPG/n-C₈ denotes an ester of neopentyl glycol and the normal organicacid (the straight-chain fatty acid) having 8 carbon atoms. In the caseof NPG/2EH, 2EH is an abbreviation of 2-ethylhexanoic acid and NPG/2EHdenotes an ester of neopentyl glycol and 2-ethylhexanoic acid.

1) As shown in Examples 1 to 4, the esters of neopentyl glycol (NPG) areesters of neopentyl glycol as dihydric alcohol and a monocarboxylic acidas monobasic organic acid, and are characterized by containing two estergroups in the molecule. Such a chemical structure has an importantbearing on the miscibility with flon 134 a and the viscositycharacteristics of the oils.

That is, ester oils of a monocarboxylic acid having 7 to 8 carbon atomswere satisfactory and had a lower critical solution temperature of −29°C. to −70° C. and a viscosity at 40° C. of 2.8 to 7.0 cSt.

The smaller the number of carbon atoms of the monocarboxylic acid (thefatty acid), the lower the lower critical solution temperature. It wasfound that the lower critical solution temperature of the ester of2-ethylhexanoic acid (2EH) of Example 3 and the ester of isoheptanoicacid (i-C₇) of Example 4 which have a branched chain in the molecule isadvantageously lower than that of the esters of Examples 1 and 2,respectively. The case of increasing the number of carbon atoms of thecarboxylic acid to 11 for increasing the viscosity is Example 5. Theester of Example 5 was found to have a viscosity at 40° C. of 14.9 cStand a lower critical solution temperature of −40° C. at the lowest.

2) Next, the esters of trimethylolpropanol (TMP) containing three esterlinkages in the molecule are explained below with reference to Examples6 to 10.

The ester oils obtained by the condensation of trimethylolpropane (TMP)as trihydric alcohol and a monocarboxylic acid as monobasic organic acidcontain three ester groups in the molecule, and the monocarboxylic acidhas 6 to 8 carbon atoms. The ester oils have a viscosity at 40° C. of10.8 to 32.2 cSt and a lower critical solution temperature of −20° C. to−60° C. Of these ester oils, ester oils having a lower critical solutiontemperature of −20° C. or lower are the ester oil of heptanoic acid(n-C₇) of Example 6, the ester oil of octanoic acid (n-C₈) of Example 8and the ester oil of 2-ethylhexanoic acid (2EH) of Example 9. Ester oilshaving a lower critical solution temperature of −60° C. or lower are theester oil of hexanoic acid (n-C₆) of Example 7 and the ester oil ofisoheptanoic acid (i-C₇) of Example 10. The ester oils of Examples 6 to10 are also characterized in that the smaller the number of carbonatoms, the lower the lower critical solution temperature, and that thelower critical solution temperature of the ester oils containing abranched chain is lower than that of the ester oils containing nobranched chain even when the former ester oils and the latter ester oilshave the same number of cabon atoms.

3) As shown in Examples 11 to 13, the ester oils obtained by thecondensation of pentaerythritol (PET) as tetrahydric alcohol and amonocarboxylic acid contain 4 ester groups in the molecule, and themonocarboxylic acid has 6 to 8 carbon atoms. The ester oils have a highviscosity at 40° C. of 17.5 to 52.0 cSt and a lower critical solutiontemperature of −8° C. to −44° C. Thus, the lower critical solutiontemperature is shifted to higher temperatures, as compared with theabove-mentioned ester oils of dihydric alcohols and trihydric alcohols.Of the ester oils of Examples 11 to 13, ester oils having a lowercritical solution temperature of −40° C. or lower are the ester oil ofhexanoic acid (n-C₆) of Example 11 and the ester oil of isoheptanoicacid (i-C₇) of Example 13. The ester oils of Examples 11 to 13 are alsocharacterized in that the smaller the number of carbon atoms, the lowerthe lower critical solution temperature, and that the lower criticalsolution temperature of the ester oils containing a branched chain islower than that of the ester oil containing no branched chain.

4) As a method for introducing 4 ester groups into the molecule, thereis a method in which esterification is carried out by condensing apolyhydric alcohol and a monocarboxylic acid with a dicarboxylic acid(i.e. a typical dibasic organic acid) as the central constituent. Bythis method, the lower critical solution temperature can easily belowered and the viscosity can easily be increased. Esters obtained bysuch a molecular design are complex esters and are explained withExamples 14 to 17 of the present invention.

Example 14 shows a complex ester of glutaric acid (abbreviated as Glut)as dicarboxylic acid, neopentyl glycol (NPG) as dihydric alcohol, andhexanoic acid (C₆) as monocarboxylic acid. This complex ester had aviscosity at 40° C. of 32.6 cSt, a viscosity at 100° C. of 5.9 cSt, anda lower critical solution temperature of −75° C. or lower.

Example 15 shows the case where an ester having moderate viscosity gradewas prepared by mixing the esters of Examples 4 and 16. This ester wasalso found to possess a lower critical solution temperature not muchchanged.

Example 16 shows a complex ester of adipic acid (abbreviated as AZP) asdicarboxylic acid, neopentyl glycol (NPG) as dihydric alcohol, anddecanoic acid (n-C₁₀) as monocarboxylic acid. Example 17 shows a complexester of glutaric acid (Glut) as dicarboxylic acid, neopentyl glycol(NPG) as dihydric alcohol, and isohexanoic acid (i-C₆) as monocarboxylicacid. These complex esters were found to be so excellent that they had aviscosity at 40° C. of 54.5 to 56.6 cSt, a viscosity at 100° C. of 7.3to 8.6 cSt, and a lower critical solution temperature of −60° C. Theseresults indicate that a complex ester having a suitable viscosity can besynthesized by determining properly the number of carbon atoms (C₂ toC₁₀) of a dicarboxylic acid as dibasic organic acid and the number ofcarbon atoms (C₅ to C₁₀) of a monocarboxylic acid as monobasic acid, andcondensing the dicarboxylic acid, the monocarboxylic acid, and apolyhydric alcohol in a properly chosen molar ratio.

When these Examples are arranged, the esters can be represented asfollows by general formulas:

Esters of neopentyl glycol:

(R₁-CH₂)₂-C-(CH₂OCOR₂)₂  (1)

Esters of trimethylolalkane:

R₁-CH₂-C-(CH₂OCOR₂)₃  (2)

Esters of pentaerythritol:

C-(CH₂-OCOR₂)₄  (3)

Complex esters:

In addition, examples of easily obtainable esters are esters ofdipentaerythritol:

(R₂COOCH₂)₃C—CH₂-O—CH₂-C(CH₂-OCOR₂)₃  (5)

In the above formulas (1) to (5), R₁ is H or an alkyl group having 1 to3 carbon atoms, R₂ is a straight-or branched-chain alkyl group having 5to 12 carbon atoms, R₃ is an alkyl group having 1 to 3 carbon atoms, andn is an integer of 0 to 5.

The viscosity could be optionally determined by choosing the kinds ofthe polyhydric alcohol and the carboxylic acid(s).

A moderate viscosity could easily be attained by blending alow-viscosity oil and a high-viscosity oil.

In the case of a refrigerating apparatus using a flon type refrigerantcontaining no chlorine, for example, flon 134 a, a refrigerating machineoil capable of imparting fundamentally satisfactory performancecharacteristics and reliability to a compressor and the refrigeratingapparatus can be obtained by selecting an oil having a lower criticalsolution temperature of 0° C. or lower (the first target value) or anoil having a lower critical solution temperature of −30° C. or lower(the second target value) both of which have a viscosity at 40° C. of 2to 70 cSt, preferably 5 to 32 cSt and a viscosity at 100° C. of 1 to 9cSt, preferably 2 to 6 cSt, from the hindered esters and the complexesters which contain two or more ester linkages in the molecule.

It was confirmed that these ester type refrigerating machine oils have agood miscibility not only with flon 134 a but also with all flon typerefrigerant gases containing no chlorine, for example, flon 152 a(difluoroethane CH₃CHF₂). The refrigerating machine oils were effectivein imparting high performance characteristics and a high reliability toa refrigerating apparatus.

In addition, it was confirmed that since these ester oils according tothe present invention are highly soluble also in conventionalchlorine-containing flon type refrigerants (chlorofluorohydrocarbon typerefrigerants) such as flon 12 and flon 22, they are effective also whenused in part in admixture with these refrigerants.

However, since the conventional chlorine-containing flon typerefrigerants are included in the list of compounds under regulation inuse because of the problem of environmental disruption, it is preferableto adjust the proportion of the refrigerants to 50% or less and that ofthe ester oil according to the present invention to 50% or more.

Next, an example of refrigerating apparatus for achieving the secondobject of the present invention is given below.

EXAMPLE 18

The rotary compressor shown in FIG. 7 which was a refrigerant compressorwas incorporated into a refrigerating apparatus having the constitutionshown in FIG. 9. At a compressor temperature of 100° C. and a dischargedgas pressure of 9.5 to 10 kgf/cm²G which were conditions of examiningthe reliability of a refrigerator, a relationship between the viscosityof a refrigerating oil stored in the compressor and the coefficient ofperformance (COP), i.e., the ratio of the refrigerating capacity of thecompressor to an input, was measured by using some of the ester oilswith a typical viscosity grade exemplified in Table 1. The resultsobtained are shown in FIG. 3.

FIG. 3 shows a relationship between the actual viscosity of eachrefrigerating machine oil and the coefficient of performance (COP) whichwas determined for the ester oils according to the present inventionhaving a viscosity at 40° C. of 5 to 56 cSt and conventional examples,i.e., a polyalkylene glycol and an alkylbenzene oil (SUNISO Z-300A) usedin combination with flon 12. In FIG. 3, the axis of abscissa refers tothe actual viscosity of each refrigerating machine oil stored in therotary compressor, and the axis of ordinate to the coefficient ofperformance (expressed in terms of a relative value) of the compressor.

According to FIG. 3, when refrigerating machine oils are compared in thecoefficient of performance by taking the coefficient of performanceattained by the conventional combination of flon 12 and Z-300A (analkylbenzene oil) having a viscosity at 40° C. of 56 cSt, as 1.0, thecoefficient of performance attained for the combination of thepolyalkylene glycol (PAG56) of Conventional Example 3 and flon 134 a isas small as 0.859, indicating that the energy efficiency is lowered byabout 14%.

On the other hand, the complex ester according to the present inventionwith a viscosity at 40° C. of 56.6 cSt of Example 17 gave a satisfactorycoefficient of performance of 0.906. It can be speculated that thisresult is attributable to a reducing effect on friction loss caused onthe basis of the journal bearing theory represented by the theory of theformula (9), a reducing effect on oil-agitating power, aheat-dissipating effect, etc. which are brought about because theviscosity of the refrigerating machine oil which contains flon 134 adissolved therein becomes as low as 4.35 cSt under the same operationconditions.

When the ester oils according to the present invention which had a stilllower viscosity of 5 to 32 cSt (at 40° C.) were compared in thecoefficient of performance under the same conditions, the ester oil witha viscosity of 32.6 cSt (at 40° C.) of Example 14, the ester oil with aviscosity of 14.9 cSt (at 40° C.) of Example 5 and the ester oil with aviscosity of 14.9 cSt (at 40° C.) of Example 10 gave coefficient valuesof 0.926, 0.966 and 0.973, respectively. Thus, the coefficient ofperformance was increased in that order. On the other hand, in the caseof the ester oil with a viscosity of 5.5 cSt (at 40° C.) of Example 4,the coefficient of performance was 0.953, namely, it showed a tendencyto be decreased a little.

From these results, it can be seen that an ideal ester oil suitable forthe rotary compressor is an ester oil which has a viscosity at 40° C. inthe range of 5 to 32 cSt (exactly, 5.5 to 32.6 cSt), i.e., a rangearound the most suitable value of 14.9 cSt, and contains two or moreester linkages in the molecule, as described above.

EXAMPLE 19

Flon 134 a and each of the refrigerating machine oils according to thepresent invention exemplified in Table 1 were used in a low-pressurevessel type reciprocating compressor, and the compressor wasincorporated into a refrigerator, i.e., a refrigerating apparatus. Therefrigerator was then subjected to a high-temperature reliability test(pressure in case 1.6 kg/cm² abs, case temperature 85° C., 100 V, 50Hz).

FIG. 4 shows the test results. In this graph, the axis of abscissarefers to the measured value of viscosity of the refrigerating machineoil, and the axis of ordinate to the coefficient of performance (COP).The graph was obtained by plotting the coefficient of performanceagainst the actual viscosity in actual operation of each of the samplerefrigerating machine oils with a viscosity at 40° C. of 5.5, 14.9,22.0, 32.6 and 56.6 cSt, respectively, shown in Examples in Table 1. Thecoefficient of performance is in linear relation with the actualviscosity.

From the results shown in FIG. 4, it can be seen that the lower theviscosity of the refrigerating machine oil, the larger the coefficientof performance of the low-pressure vessel type reciprocating compressor.The refrigerating machine oils having an actual viscosity of 2 to 4.2cSt and a viscosity at 40° C. of 5.5 to 14.9 cSt can be said to beexcellent. When the actual viscosity is less than 2 cSt, a decrease ofthe coefficient of performance and a lowering of the reliability ofbearings tend to be caused because in the case of using a conventionalmaterial such as cast iron or an iron-based sintered material forproducing the sliding parts of the compressor, the precision offinishing the surfaces of the sliding parts is limited, and therefore attoo low an actual viscosity, the lubrication on the surfaces gets intothe so-called boundary lubrication region in which the contact betweenmetal surfaces occurs.

EXAMPLE 20

The lubrication in a refrigerating machine and a refrigerant compressorfor achieving the third object of the present invention is explainedbelow with reference to the following example.

For evaluating the lubrication, there were carried out a FALEX test inwhich a seizing load was measured in the air, and a high-pressureatmosphere friction test in which a seizing load was measured in arefrigerating machine oil containing 50% of flon 134 a dissolvedtherein. FIG. 5 is a graph showing the correlation between the resultsof the two tests. The seizing load is as follows. An increasing load wasapplied to a rotating sample pin from both sides and a load at whichseizing was caused was expressed in pound (lb).

In the present example, the ester oil of trimethylolpropane (TMP) andisoheptanoic acid (i-C₇) of Example 10 exemplified in Table 1 wasemployed as a typical example of a refrigerating machine oil used in therefrigerating apparatus of the present invention, and there wasdetermined a relationship between the kind and amount of an extremepressure agent added to the ester oil and the lubricatingcharacteristics. As to materials for test pieces used for the evaluationof the lubrication, the materials for the pin and a block were standardmaterials, i.e., SNC-21 (nickel chrome steel) according to the standardof JIS and SUM 41 (resulfurized free-cutting steel) according to thestandard of JIS, respectively. On the other hand, in the high-pressureatmosphere friction test, there was measured a load at which seizing wascaused by friction between cylinders made of a material for shaft(eutectic graphite cast iron) and a material for roller (eutecticgraphite cast iron tempered material), respectively, which had givensatisfactory results in rotary compressors.

As shown in the case of sample No. 1 in FIG. 5, the ester oil (the oilof Example 10) containing no extreme pressure agent gave a FALEX seizingload of 700 lb and a seizing load of as low as 90 kgf/cm² in a flon 134a atmosphere. On the other hand, in the case of sample No. 2 and sampleNo. 3, the FALEX seizing load was further increased by 400 lb to reach1100 lb and the seizing load in a flon 134 a atmosphere was increased by90 kg/cm² to reach 180 kg/cm², owing to addition of each of thefollowing extreme pressure agents. In the case of sample No. 2, CHELEXH-10 (a trade name, mfd. by SAKAI CHEMICAL INDUSTRY Co., Ltd.) which wasan acidic phosphoric acid containing an active OH group in the molecule,was added in an amount of 1%. In the case of sample No. 3, an estercompound of an alkylene glycol and phosphoric acid(butylpolyoxypropylene phosphate ester) was added in an amount of 1%.

That is, it was actually proved that the phosphorus-containing compoundssuch as the acidic phosphoric ester and the alkylene glycol phosphateester compound act effectively as extreme pressure agents for preventingseizing, regardless of the presence of flon 134 a.

Next, a FALEX test was carried out continuously for a maximum time of120 minutes while keeping an applied load constant at 100 lb, and theabrasion loss of a pin, i.e., an iron-based test piece, was measured.The results obtained are shown in FIG. 6. In the case of the oil ofsample No. 4 which contained no extreme pressure agent, the pin was wornin an amount of 25 mg. On the other hand, in the case of both of theoils containing each of the above-mentioned phosphorus-containingcompounds, the abrasion loss was as small as 0.4 mg as shown for sampleNo. 7 and sample No. 8, namely, the abrasion loss could be reduced toone-fifth or less. The amount of the phosphorus-containing compoundadded is effective from about 0.05 wt % as shown for sample No. 5. Theeffect of the compound is increased with an increase of the amount. Butwhen the amount exceeds 10 wt %, the improving effect on the lubricationhits the ceiling, so that the addition of the compound becomeseconomically disadvantageous and hence becomes unpractical.

The abrasion loss could be reduced by increasing the viscosity of oilfrom 14.9 cSt (at 40° C.) of sample No. 4 to 56.6 cSt (40° C.) of sampleNo. 6.

From the facts described above, it was found that the seizing load,abrasion resistance and lubrication of the iron-based sliding memberscould be greatly improved by adding a phosphorus-containing compoundsuch as an acidic phosphoric ester, phosphoric ester, alkylene glycolphosphate ester or the like as an extreme pressure agent to therefrigerating machine oil used in the present invention, in an amount of0.05 to 10 wt %, or by adjusting the viscosity of the oil to a highvalue instead of adding the extreme pressure agent. The refrigeratingmachine oil which contains the extreme pressure agent exhibits excellentperformance characteristics particularly in the presence of a flon typerefrigerant containing no chlorine, such as flon 134 a.

EXAMPLE 21

An example for achieving the fourth object of the present invention isdescribed below. The behaviors of electrical insulating materials usedin the hermetic motor of a compressor, in the presence of both flon 134a and the refrigerating machine oil according to the present inventionwere evaluated. The results obtained are explained below with referenceto Table 2 and Table 3.

Flon 134 a and refrigerating machine oils were evaluated by observingthe degree of deterioration of characteristics of a magnet wire (anenameled wire) and an insulating film material by a sealed tube test,for preventing external influence.

(1) Insulating Characteristics Of A Magnet Wire (An Enameled Wire)

As magnet wire test pieces, two kinds of test pieces, i.e., 5% elongatedproducts and twisted-pair test pieces were subjected to a sealed tubetest at 150° C. for 40 days. An explanation is given below withreference to the results shown in Table 2.

As a result of the sealed tube test carried out for a combination offlon 134 a and the polyalkylene glycol listed as Conventional Example 3in Table 1 which is a refrigerating machine oil said to be suitable forflon 134 a, 5% elongated products of both the polyester wire (PEW) ofsample No. 9 and the ester imide wire (EIW-R) of sample No. 10 in Table2 were crazed, and the retention of the dielectric breakdown voltage oftwisted-pair test pieces of these two kinds of wires was greatly loweredto 30 to 32%.

On the other hand, the same evaluation as above was carried out for acombination of flon 134 a and the composite ester oil composed ofglutaric acid (Glut), neopentyl glycol (NPG) and isohexanoic acid (i-C₆)which is a refrigerating machine oil used in the present invention andis exemplified in Table 1. Consequently, the same polyester wire (whoseglass transition temperature is shown in Table 2) and polyester imidewire as the wires which were described above and deteriorated asconventional examples sample No. 9 and sample No 10, showed noabnormality in appearance, as shown for sample No. 11 and sample No. 12.The retention of the dielectric breakdown voltage of these samples wasas high as 95% or more, indicating that the degree of deterioration ofthe magnet wires was very low. The reason is as follows. Therefrigerating machine oil according to the present invention has a lowwater content in the early stages and a high thermal stability, andhardly produce an acidic substance capable of accelerating hydrolysis,and these characteristics bring about the improving effects.

Sample No. 13 was obtained by coating the ester imide wire of sample No.12 with a polyimide layer to form a composite. Sample No. 14 was a wirecoated with a polyamide-imide alone (AIW). Both samples had satisfactorycharacteristics. It was found that such a magnet wire obtained by thuscoating a layer with a high glass transition temperature on a layer witha low glass transition temperature contributes to the improvement of thereliability of a compressor because the upper coating layer is effectiveas protective layer against an attack of flon 134 a and therefrigerating machine oil.

(2) Insulating Characteristics Of Insulating Films

As a sealed tube test on insulating films for motor, an insulatingstrength test at 130° C. for 40 days was carried out, whereby the filmswere evaluated with respect to the appearance and the retention oftensile strength. The results obtained are shown in Table 3.

When a polyester film (Lumilar X₁₀, a trade name, mfd. by TorayIndustries, Inc.) conventionally used in the hermetic motor of acompressor was used in the conventional polyalkylene glycol oil shownfor sample No. 15, its oligomer component was precipitated in the oiland the retention of tensile strength was 83%.

On the other hand, in a combination of the complex ester oil of Example17 according to the present invention and flon 134 a, no oligomer wasprecipitated and the retention of tensile strength was as high as 89% ormore in the case of all of Lumilar X₁₀ of sample No. 16, PA-61M (a tradename, mfd. by Hitachi Kasei Co., Ltd.), i.e., the polyamide-imide-coatedpolyester of sample No. 17, the polyphenylene sulfide (PPS) film ofsample No. 18, and the polyether ether ketone (PEEK) film of sample No.19. Thus, it was found that the electrical insulating system of acompressor using flon 134 a can be markedly improved in reliability.

That is, it was found that the insulation system of a hermetic motor canbe completed by properly selecting a film from the group consisting ofpolyester films, polyamide-imide-coated polyester films, PPS films andPEEK films which have a glass transition temperature of 65° C. orhigher, and using the same in the presence of both flon 134 a and therefrigerating machine oil containing two or more ester groups in themolecule according to the present invention. It was found that when theinsulation system is thus completed, there can be solved the problem ofprecipitation of an oligomer component (the problem described above forthe oil of Conventional Example 3 shown for sample No. 15), the problemsin the performance characteristics of a compressor and a refrigeratingapparatus which are caused by the lowering of the film strength, and thepractical problems in the long-term reliability.

TABLE 2 Results of evaluating performance characteristics with respectto resistance to Glass an oil and flon 134a transition AppearanceRetention of Sample Insulation-coated temperature change dielectricbreakdown No. winding wire (° C.) Oil tested (Note 1) voltage (Note 2) 9 PEW 120-140 Conventional Clazed 30 (Polyester) Example 3 10 EIW-R190-210 Conventional ″ 32 (Polyester imide) Example 3 11 PEW 120-140Example 17 No 95 (Polyester) abnormality 12 EIW-R 190-210 ″ No 98abnormality 13 RFW-V (Upper layer Lower layer ″ No polyamide/lower layer190-210 abnormality 98 polyester imide) Upper layer 250-310 14 AIW250-310 ″ No 98 (Polyamide imide) abnormality Sealed tube test: 150° C.× 40 days Note 1: 5% elongated wire Note 2: A relative value obtainedfor a twisted pair test piece by dividing a value after the test by avalue before the test (taken as 100).

TABLE 3 Results of evaluating performance characteristics with respectto resistance to Glass an oil and flon 134a transition Retention ofSample temperature Appearance tensile strength No. Insulating film (°C.) Oil tested change (Note 1) 15 Lumilar × 10 65 Conventional Oligomerwas 89 (polyester) Example 3 precipitated 16 Lumilar × 10 65 Example 17None 89 17 PA-61M 65 ″ None 90 (Polyamide-imide- coated polyester) 18PPS (Polyphenylene 85 ″ None 95 sulfide) 19 PEEK (Polyether ether 143  ″None 98 ketone) Sealed tube test: 130° C. × 40 days Note 1: A relativevalue obtained by dividing a value after the test by a value before thetest (taken as 100).

EXAMPLE 22

An example for achieving the fifth object of the present invention isdescribed below.

It is known that particularly in refrigerating apparatus using a heatexchanger at 0° C. or lower, the control of water content in therefrigerating apparatus has an important influence on the coolingcapability and the assurance of the quality of an electrical insulatingmaterial. Therefore, the establishment of a technique for removing wateris indispensable for the system of the refrigerating apparatus.

In a refrigeration cycle composed as shown in FIG. 9, flon 134 a gasdischarged from a compressor 40 is condensed into a liquid refrigerantby heat dispersion in a condenser 41. This high-temperature,high-pressure liquid refrigerant is transformed into low-temperature,low-pressure wet vapor by an expansion mechanism 42 and sent to anevaporator 43. In this series of steps, the water in the refrigeratingapparatus is adsorbed and removed by a drying agent represented bysynthetic zeolite in a dryer 45 provided between the condenser 41 andthe expansion mechanism 42. It is important to choose the kind of thedrying agent in consideration of a use environment in which therefrigerating machine oil according to the present invention and flon134 a coexist. The suitability of the drying agent is explained belowwith reference to Examples shown in Table 4.

Drying agents tested are synthetic zeolites having trade names ofMolecular Sieves all manufactured by UNION SHOWA K.K. These syntheticzeolites are classified according to the adsorption capacity (%) at 25°C. and at a carbon dioxide gas partial pressure of 250 mmHg which isused as an indication of the distribution of the diameter of pores foradsorption.

As to the suitability of the synthetic zeolites for flon 134 a and therefrigerating machine oil according to the present invention, theresults of a sealed tube test shown in Table 4 are explained below.

It was found that the synthetic zeolite composed mainly of sodiumaluminate and sodium silicate shown as sample No. 20 (a conventionalexample; trade name 4ANRG) has a fluorine ion adsorption of as large as1.05%, so that problems due to the lowering of the strength or formationinto powder are caused by the reaction of the synthetic zeolite. SampleNo. 21 (a comparative example; trade name 4AXH-6) and sample No. 22 (acomparative example; trade name XH-7) which are composed mainly ofsodium aluminate, potassium aluminate, sodium silicate and potassiumsilicate have a carbon dioxide gas adsorption capacity of 4.5 to 1.5%and a reduced fluorine ion adsorption of 0.24%. But, they cannot putinto practical use because their fluorine ion adsorption is still toolarge.

Sample No. 23 (an example; trade name XH-600) and sample No. 24 (anexample; trade name XH-9) which consist of a synthetic zeolite composedmainly of potassium aluminate, sodium aluminate, potassium silicate andsodium silicate have a carbon dioxide gas adsorption capacity of 0.2%and a greatly reduced fluorine adsorption of 0.04%. Since a fluorine ionadsorption which permits practical use is 0.1% or less, the value of0.2% indicates that these samples are sufficiently usable.

The deterioration of characteristics of a synthetic zeolite itself bythe adsorption of molecules of flon 134 a is dependent on thedistribution of pore diameter of the synthetic zeolite. It has beenconfirmed that for adjusting the fluorine ion adsorption to 0.1% orless, the employment of a synthetic zeolite whose carbon dioxide gasadsorption capacity has been adjusted to 1.0% or less is sufficient.That is, the following was found. When a synthetic zeolite composed ofalkali metal silicates and alkali metal aluminates whose carbon dioxidegas adsorption at 25° C. and at a carbon dioxide gas partial pressure of250 mmHg has been adjusted to 1.0% or less, for example, MolecularSieves XH-600 or XH-9 (trade names, mfd. by UNION SHOWA K.K.), is usedas a drying agent in a refrigerating apparatus using flon 134 a and therefrigerating machine oil containing two or more ester linkages in themolecule according to the present invention, which are placed together,only water can be effectively removed and fluorine ion adsorption hardlyproduce influences such as formation into powder or a lowering of thestrength of beads, and therefore such a drying agent is very excellentfor practical purposes.

TABLE 4 Sealed tube test* CO₂ adsorption Decomposition capacity (%) rateof Fluorine ion Sample Drying agent CO₂ partial pressure refrigerantadsorption No. Name of sample 250 mmHg (25° C.) (%) (%) 20 4ANRG 12.0 0.028 1.05 21 4AXH-6 4.5 0.032 0.24 22 XH-7 1.5 0.035 0.24 23 XH-600 0.20.042 0.04 24 XH-9 0.2 0.04  0.04 Sealed tube test: 150° C., 7 days

The carbon dioxide gas adsorption capacity at 25° C. and at a carbondioxide gas partial pressure of 250 mmHg should be 1.0% or less, and itis preferably as small as possible. When it is zero %, the drying agentabsorbs water alone selectively but not fluorine ions, so that thedrying agent becomes ideal molecular sieves. The present invention isconstituted as explained above and hence has the following effects.

(1) By using the refrigerating machine oil described below, in arefrigerating apparatus comprising a compressor, condenser, dryer,expansion mechanism and evaporator and using a flon type refrigerantcontaining no chlorine and having a critical temperature of 40° C. orhigher which is represented by flon 134 a, the performancecharacteristics and reliability of the compressor and the refrigeratingapparatus can be markedly improved because the refrigerating machine oiland the refrigerant are highly miscible with each other without theirseparation into two layers in the whole temperature range where thecompressor and the refrigerating apparatus are used, and hence alubricating oil film on the shaft and bearings of the compressor and therefrigerant-heat-transferring capability of a heat exchanger areassured. The refrigerating machine oil comprises as base oil an esteroil according to the present invention which contains two or more esterlinkages in the molecule and has a refrigerating machine oil viscosityat 40° C. of 2 to 70 cSt, preferably 5 to 32 cSt and a refrigeratingmachine oil viscosity at 100° C. of 1 to 9 cSt, preferably 2 to 6 cSt.The refrigerating machine oil has a lower critical solution temperatureof 0° C. or lower or −30° C. or lower, and is used in the first target,i.e., a moderate-temperature refrigerating apparatus such as adehumidifier, or the second targer, i.e., a low-temperaturerefrigerating apparatus such as a refrigerator, respectively.

(2) Moreover, the performance characteristics and the reliability can beimproved by an improving effect on the lubrication in the slidingportions of bearings of the refrigerant compressor which is obtained byadding a phosphoric ester type extreme pressure agent having OH groupsin the molecule and other additives such as an abrasion-preventingagent, acid-capturing agent, antioxidant, defoaming agent, etc. to theabove-mentioned refrigerating machine oil.

(3) By simultaneous use of the refrigerating machine oil containing twoor more ester linkages in the molecule according to the presentinvention described below and flon 134 a, the so-called performancecharacteristics can be improved, namely, the coefficient of performanceindicating the performance characteristics of the compressor can beincreased, the power consumption of the refrigerating apparatus usingthe compressor can be reduced, and the refrigerating capacity can beincreased. In a high-pressure vessel type rotary compressor, therefrigerating machine oil is one which has a viscosity at 40° C. of 2 to70 cSt, preferably 5 to 32. In a low-pressure vessel type reciprocatingcompressor, the refrigerating machine oil is one which has a viscosityat 40° C. of 2 to 70 cSt, preferably 5 to 15 cSt.

(4) The electrical insulating performance and long-term reliability ofthe refrigerating apparatus can be markedly improved by using aninsulation-coated winding wire with a glass transition temperature of120° C. or higher and an insulating film with a glass transitiontemperature of 70° C. or higher as insulating materials for a motor, anda refrigerating machine oil comprising as base oil the ester oilaccording to the present invention, in a refrigerant compressor using aflon type refrigerant containing no chlorine represented by flon 134 a.

(5) By using a synthetic zeolite composed of alkali metal silicates andalkali metal aluminates having a carbon dioxide gas adsorption capacityat 25° C. and at a carbon dioxide gas partial pressure of 250 mmHg of1.0% or less, in the dryer constituting the refrigerating apparatus,water in the refrigeration cycle can be efficiently separated andadsorbed, and there can be prevented troubles caused by formation of thedrying agent into powder by deterioration of the drying agent itself,namely, the problems caused by clogging of a piping for refrigerant withthe drying agent and abnormal abrasion due to intrusion of the dryingagent into the sliding portions of the compressor. Therefore, theemployment of the synthetic zeolite has a marked improving effect on theperformance characteristics and the long-term reliability.

(6) The refrigerating apparatus having the constitution explained abovecan reduce the ozone depletion potential (ODP) and the global warmingpotential (GWP) which are in question in the terrestrial environment tozero and 0.3 or less, respectively, relative to values attained when aconventional chlorine-containing flon type refrigerant gas (e.g. flon12) is used.

What is claimed is:
 1. A refrigeration cycle comprising at least a compressor, a condenser, an expansion mechanism, and an evaporator, a refrigerant in said cycle composed of a hydrofluorocarbon refrigerant containing no chlorine atoms and having a critical temperature of 40° C. or higher, and a refrigerating machine oil comprising as base oil a hindered ester oil of one or more fatty acids wherein the ester oil contains at least two ester linkages

in the molecule, said refrigerating machine oil dissolving the refrigerant therein having an actual viscosity of 1.0 to 4.0 cSt when measured at a gas pressure of 9 to 11 kg/cm² abs and an oil temperature of 100° C., said compressor being a high-pressure closed vessel.
 2. A refrigeration cycle according to claim 1, wherein the refrigerating machine oil has a viscosity of 2 to 70 cSt at 40° C.
 3. A refrigeration cycle according to claim 1, wherein the hindered ester oil comprises at least one member selected from the group consisting of ester oils represented by the following general formulae (1) to (4): (R₁CH₂)₂C(CH₂OCOR₂)₂ (1) R₁CH₂C (CH₂OCOR₂)₃ (2) C(CH₂OCOR₂)₄ (3) and (R₂COOCH₂)₃CCH₂OCH₂C(CH₂OCOR₂)₃ (4)

wherein R₁ is H or an alkyl group having 1 to 3 carbon atoms, and R₂ is a straight or branched-chain alkyl group having 5 to 12 carbon atoms.
 4. A refrigeration cycle according to claim 1, wherein said compressor has a motor having a stator and a rotor to compress the refrigerant, said stator having a winding wire and an insulating film, said winding wire comprising a core wire having an enamel coating having a glass transition temperature of 120° C. or higher.
 5. A refrigeration cycle according to claim 4, wherein said insulating film comprises a crystalline plastics film having a glass transition temperature of 50° C. or higher.
 6. A refrigeration cycle according to claim 4, wherein said enamel coating is at least one member selected from the group consisting of polyesters, polyester imides, polyamides and polyamide-imides.
 7. A refrigeration cycle according to claim 4, wherein said insulating film comprises at least one film made of a material selected from the group consisting of polyethylene terephthalates, polybutylene terephthalates, polyphenylene sulfides, polyether ether ketones, polyethylene naphthalates, polyamide-imides, polyamide-imide coated polyesters, polyesters and polyimides.
 8. A refrigeration cycle comprising at least a compressor, a condenser, an expansion mechanism, and an evaporator, a refrigerant in said cycle composed of a hydrofluorocarbon refrigerant containing no chlorine atoms and having a critical temperature or 40° C. or higher, and a refrigerating machine oil comprising as base oil a hindered ester oil of one or more fatty acids wherein the ester oil contains at least two ester linkages

in the molecule, said refrigerating machine oil dissolving the refrigerant dissolved therein having an actual viscosity of 2.0 to 4.5 cSt when measured at a gas pressure of 1.0 to 2.0 kg/cm² abs and an oil temperature of 85° C., said compressor being a low pressure closed vessel.
 9. A refrigeration cycle according to claim 8, wherein the refrigerating machine oil has a viscosity of 5.0 to 15 cSt at 40° C.
 10. A refrigeration cycle according to claim 8, wherein the hindered ester oil comprises at least one member selected from the group consisting of enter oils represented by the following general formulae (1) to (4): (R₁CH₂)₂C(CH₂OCOR₂)₂ (1) R₁CH₂C (CH₂OCOR₂)₃ (2) C(CH₂OCOR₂)₄ (3) and (R₂COOCH₂)₃CCH₂OCH₂C(CH₂OCOR₂)₃ (4)

wherein R₁ is H or an alkyl group having 1 to 3 carbon atoms, and R₂ is a straight or branched-chain alkyl group having 5 to 12 carbon atoms.
 11. A refrigeration cycle according to claim 8, wherein said compressor has a motor having a stator and a rotor to compress the refrigerant, said stator having a winding wire and an insulating film, said winding wire comprising a core wire having an enamel coating having a glass transition temperature of 120° C. or higher.
 12. A refrigeration cycle according to claim 11, wherein said insulating film comprises a crystalline plastics film having a glass transition temperature of 50° C. or higher.
 13. A refrigeration cycle according to claim 11, wherein said enamel coating is at least one member selected from the group consisting of polyesters, polyester imides, polyamides and polyamide-imides.
 14. A refrigeration cycle according to claim 11, wherein said insulating film comprises at least one film made of a material selected from the group consisting of polyethylene terephthalates, polybutylene terephthalates, polyphenylene sulfides, polyether ether ketones, polyethylene naphthalates, polyamide-imides, polyamide-imide coated polyesters, polyesters and polyimides.
 15. A refrigeration cycle according to claim 1, wherein said refrigeration cycle further comprises a dryer.
 16. A refrigeration cycle according to claim 8, wherein said refrigeration cycle further comprises a dryer. 